Some Important Notes and Formulas for High Voltage Transmission Line

7/25/2019 Some Important Notes and Formulas for High Voltage Transmission Line

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Some Important Notes and Formulas for High Voltage

Transmission Line:

1 Wind Speed

1.1 Basic wind speed

The basic wind speeds have been worked out for 50 years return period. The basic

wind speed is based on peak gust velocity averaged over a short time interval of about

3 seconds and corresponds to 10 m height above mean sea level. The basic wind

speed for wind zone 4 is 4 m!s.

4 secbm

V =

1.2 Reference wind speed

"t is e#treme value of wind speed over an average period of 10 minutes duration and is

to be calculated from basic wind speed by the following relationships$

0

b

R

VV

k=

%here k0is a factor to convert 3 seconds peak gust speed into average speed of wind

during 10 minutes period at a level of 10 meters above ground. k0 is to be taken as

1.35.

1.3 Design wind speed

The design wind speed shall be$

1 &d RV V K K =

%here' ()* reference wind speed in m!sec

+1* )isk coefficient ,for 50 years return period +1- 1.0

+&/ Terrain roughness coefficient as per below table

Table$

(alue of +&$ategory 1/ oastal areas' 1.02ategory &/ ormal cross country lines with very few obstacles' 1.0

ategory 3/ rban built up areas areas' 0.25

age 1 sur 5


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1.4 Design wind pressure

The design wind pressure on towers conductors and insulators shall be obtained by

the following relationship$

&0.6d d

P V=

where'

d - 7esign wind pressure in !m&

(d - 7esign wind speed in m!sec

1.5 Design wind load on conductor & Groundwire

[ ]wc d c dcF P L D G C N=

%here'


8 - wind span being sum of half the span on either side of supporting

point in m

7 - 7iameter of conductor!groundwire in m

9c - 9ust response factor depends on span turbulence and height above the9round' for 400 m span and terrain category 1 and 40 m heigh tower

the 9c shall be &.00.

dc - 7rag coefficient which is 1.0 for conductor and 1.& for groundwire.

1.6 Design wind load on Tower

[ ]WT d dt eF P C A GT N=

%here'


dt - 7rag coefficient which depends on the solidity ratios &.0 to 3.6

:e - total net surface area in m&

9T - 9ust response factor

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1.7 Design wind load on nsulators

[ ]1.& Wi d iF P A Gi N=

%here'


:i - 0.5;dia of insulator;length of string in m&

9i - 9ust response factor for insulator

2 Foundation

2.1 !oncrete grade

&0 $ haracteristic strength of &0 !mm&

This strength is the minimal design strength which shall be confirmed from the cube

test.

3 Tower

3.1 Base widt"

The base width of the tower can be determined from the empirical formula$

[ ]'B k M cm=

%here'

< - =verturning moment in kg/m

+ - : constant' 1.>3

"n general the base width will be$

,1!4 to 1!6 of overall height of the tower

? is for heavy angle tower

1!5 is for medium angle tower

1!6 is for suspension tower

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3.2 nclination of #ain legs

Typical inclination of the tower legs ,with vertical for various voltages tower$

Up to 220 kV:

@uspension tower legs ,in both directions$ 40

:ngle towers ,in both directions$ 0

7ead end Towers ,in both directions$ 20

400 kV and ao!e:

@uspension tower legs ,in both directions$ 20

:ngle towers ,in both directions$ 100

7ead end Towers ,in both directions$ 11

0

3.3 $ini#u# Ground !learance

Voltage Le!el "kV# $inimum ground %learan&e "m#

66 5.5

13& 6.1

&&0 .0

400 2.2

4 Construction period

4.1 Tower erection

50 persons per month can erect 20 tonne

4.2 %tringing

50 persons per month will string & km double circuit transmission line.

age 4 sur 5


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ransmissionElineCsource-blCots-F&""+tlBn@otbIdgChl-enCsa-KCved-0cI6:Fw:Lg+ah

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age 5 sur 5

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Some Important Notes and Formulas for High Voltage Transmission Line